The invention relates to a device for monitoring a cylinder-piston assembly, and particularly a tractive force to be generated by the assembly, comprising a switch responsive to the action of the assembly.
For the cutting of a web of material, such as paperboard, into individual sections, it is known to use a crosscutter whose two blade drums are driven with periodically changing angular velocities through a linkage to produce, depending on their settings, sections of material of different lengths. For variation of the angular velocity of the blade drums, the linkage has a double crank drive with a two-armed lever (double lever) whose pivot is adapted to be shifted transversely for adjustment of the rate of change of the angular velocity. To this end, the pivot of the two-armed lever is supported in a slide, which after having been positioned in accordance with the desired length of the material section, is clamped in place. Such clamping requires a clamping force of from 30 to 40 tons.
To produce this force, it is known to clamp the slide between two eccentrics, each of which is integral with a lever. Disposed between the free ends of the two levers is a cylinder-piston assembly which exerts a tractive force which pulls the lever ends toward each other, thus producing the requisite clamping force. An insufficient clamping force must be precluded with a high degree of reliability, as otherwise the slide will be displaced by the action of the driving forces, with the linkage then reaching extreme positions. With the rate of change of the angular velocity set at a low value and the rotative speed set at the maximum permissible value, the result would be that at constant rotative speed and the now substantially increased rate of change of the angular velocity, the linkage would be destroyed.
Heretofore it was sought to provide for sufficient clamping force by causing the cylinder stroke to actuate a switch so that the machine could not be operated when the cylinder stroke was too short. With this arrangement, it could happen, especially after the crosscutter had been in operation for an extended period, that as a result of the cumulative play between the various machine parts, the piston stroke would be sufficient for actuation of the switch and yet an adequate clamping force could not be produced.